The present invention is directed generally to novel systems and methods for performing sputter deposition, and to optical devices manufactured using such systems and methods.
The present invention relates to ion beam sputter deposition (IBSD). More particularly, the present invention concerns a system and method for performing sputter deposition using a divergent ion beam source. It is believed that IBSD is a technique common in the manufacturing of optical filters.
The method is normally carried out in a vacuum environment by bombarding a target with an ion current. The bombardment results in the dislodging of atoms from the target which are then deposited as a film on a substrate. IBSD is an improvement over other types of sputter deposition techniques because it produces films that are of high quality with improved adhesive properties. IBSD produces films that have a density very similar to the bulk density of the materials used and a surface roughness which is equal to that of a super-polished substrate. These results are advantageous for optical coatings.
Performance of optical filters is further improved with deposition thickness that is uniform across the substrate. The disclosed process provides such an improvement.
In accordance with a first aspect, the present invention is directed to a system and method for simultaneously performing sputter deposition on a plurality of planar substrates. An ion current source generates an ion beam in which ions are directed toward a target. The target is formed from a first section of a sphere. Each of the plurality of planar substrates has a deposition surface that is tangent to a surface of other sections of the same sphere. In one embodiment, the plurality of planar substrates are arranged as a mosaic of tiles arranged generally about the surface of another section(s) of the sphere. As a result of the spherical shape of the target and the arrangement of the planar substrates on the surface of the same sphere, substrates that are small compared to the radius of the sphere receive a substantially uniform deposition thickness that is substantially the same for each of the plurality of planar substrates. In accordance with further embodiments, a plurality of targets each of which is formed from a section of the sphere are used, and the target is negatively biased during operation of the system.
In accordance with a still further aspect, the present invention is directed to a system and method for performing sputter deposition on a spherically-shaped substrate. In this embodiment, an ion current source generates an ion beam in which ions are directed toward a target (e.g., a negatively biased target) that is formed from a first section of a sphere. A spherically-shaped substrate is disposed along a second section of the same sphere. As a result of the spherical shape of the substrate and its positioning on the same sphere as the spherically-shaped target, the deposition thickness distribution over the spherically-shaped substrate remains substantially uniform during operation of the system.
In an embodiment useful for affecting uniform wear of the target during operation of the either of the systems described above, the ion current source used for implementing the system is a divergent ion beam source that generates a divergent ion beam, and the discharge surface of the ion source is placed on the surface of the sphere in which the spherically-shaped target lies. The divergent ion beam source has a central axis positioned along a radius of the sphere. The ion current produced by the divergent ion beam source varies throughout the divergent ion beam in accordance with (or substantially in accordance with) the equation:
xe2x80x83ion current=J0 cos (xcex8);
where xcex8 is an angle between the central axis and a direction of the ion current, and J0 is an ion current density along the central axis. In this embodiment, the ion current density arriving at each portion of the spherically-shaped target is substantially identical, which in certain circumstances (e.g., a low energy ion source and a large negative bias on the target) will produce a uniform sputtering rate over the target surface.
The present invention is further directed to an optical filter that results from the practice of the disclosed systems and methods.